It is well known to provide an air bag assembly including an inflatable air bag cushion for protecting the occupant of a transportation vehicle. In an automotive vehicle such air bag assemblies are typically located within the hub of the steering wheel and in a recess in the vehicle instrument panel for protection of the vehicle occupants seated in opposing relation to such assemblies. Additional air bag assemblies may be located within the seats and/or door panels for protection of the occupants during a side impact event. It is also known to utilize inflatable curtain-like structures for deployment from the structural pillars or roofline of the motor vehicle so as to promote restraint and protection of the vehicle occupant during a roll-over event.
Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing predetermined vehicle conditions, such as a certain level of vehicle deceleration, the inflator discharges a fixed amount of inflator gas thereby forcing the air bag into a deployed position. The inflator gas occupies the available volume within the air bag cushion thereby forcing the air bag cushion to expand outwardly to the extent permitted by its construction. As inflation gas enters the air bag cushion the pressure within the cushion is increased. As the occupant comes into contact with the expanded air bag cushion, the inflator gas is forced out of the cushion thereby dissipating the kinetic energy of the occupant achieving a so-called “ride down” effect.
Traditional air bag cushions tend to project outwardly away from their storage positions in a substantially straight line during the initial stages of inflation. In a so called “top mount” or “mid mount” design, this directional projection may cause the cushion to first travel in a generally upward direction away from the air bag exit opening and against the windshield. After this initial outward projection during the latter stages of inflation such cushions assume their final inflated design profile causing them to rotate downwardly in covering relation to portions of the instrument panel below the air bag exit opening.
In order to provide additional control over the inflation characteristics of the air bag cushion it has been suggested to utilize tethering elements in the form of straps or webs extending between surfaces of the air bag cushion. These straps or webs may be released from a first restrained operative length to a second extended operative length as the depth of the air bag cushion is increased. A system incorporating such extensible tethering straps is illustrated and described in U.S. Pat. No. 5,489,119 to Prescaro et al. the contents of which are incorporated by reference as is fully set forth herein.